Correct Answer

When you use output cache on your site, it might be undesirable for you that output cache is created for every different user agent (browser), if you want to use the existing output cache for all the browsers instead of creating a new one, you will have to add the following key to your web.config file in appSetings:<add key="CMSOutputCacheItems" value="username;sitename;lang" />
The default value is set to username;sitename;lang;browser.